A military judge in Maryland has refused to drop key charges against Bradley Manning, the U.S. army soldier accused of leaking 700,000 secret documents to the anti-secrecy website WikiLeaks.

Manning already has pleaded guilty to charges of leaking the documents, charges that could get him 20 years in prison. The military judge hearing his case on Thursday turned down requests by Manning's lawyers to drop charges of aiding the enemy, which could get him a life in prison sentence if he is convicted.

His lawyers argued he never intended to help enemies of the United States, although some of the material Manning leaked was seen by the late al-Qaida leader Osama bin Laden.

In her ruling, the judge indicated the Army private, now 25 years old, should have known better. Manning was an intelligence analyst, and the judge said that because of the training he received, he would have known that terrorists had access to the leaked material on the Internet.

Manning's supporters have argued that he acted in the U.S. national interest by exposing what he believed was wrongdoing by U.S. forces during the war in Iraq - where he was deployed.

The materials he leaked included a video showing U.S. soldiers in Baghdad opening fire on a group of civilians that included journalists working for Reuters news agency.

Larry Korb, a former U.S. assistant secretary of defense and who now is an analyst with the Center for American Progress, a Washington research group, said the leaks, while illegal and embarrassing to the U.S. government, served to inform the American public.

“If you look at Iraq, there's a lot of stuff that went on there that, you know, people don't want to come out because it undermines our standing in the world, but we need to know that as Americans," said Korb.

Activists are condemning the judge's decision to keep the aiding the enemy charges against Manning, saying it could prejudge how the U.S. government will treat cases like that of former intelligence contractor Edward Snowden.

The Manning case may deter those in official positions from assuming the role of whistleblowers in the future, said Korb.

“He pleaded guilty to unauthorized disclosure. He didn't contest it. He knew what he was doing and therefore he is going to punished. So the next person has to say, 'Well, gee. If I do this, do I want to spend 20 years in jail?'”

Closing arguments come next. The judge then will issue a verdict, because Manning waived his option to have his case decided by a military jury.